The present invention relates to a process for the detoxification of effluents containing cyanide which utilizes the addition of hydrogen peroxide and either sulfur dioxide or sodium/potassium sulfite or metabisulfite.
Wastewater from a variety of industrial processes, particularly effluents generated from leaching of gold-containing ores in gold extraction plants, usually contain cyanide in various forms, such as simple cyanide and cyanide complexed with other toxic metals. In order to prevent serious damage to the environment, especially aquatic life, and to avoid an adverse impact on public health and safety, this highly toxic cyanide must be removed and/or converted into non-toxic materials before these effluents can be discharged to waterways.
Currently, several chemical processes exist for treatment of cyanide-containing effluents. See Scott, J., "An Overview of Cyanide Treatment Methods," presented at Canadian Mineral Processors 13th Annual Meeting, Ottowa, Ontario, Jan. 20-22, 1981. One of the processes involves treatment of cyanides with hydrogen peroxide. See Knorre, H., and A. Griffiths, "Cyanide Detoxification with Hydrogen Peroxide Using Degussa Process," paper presented at the Cyanide and Environment Conference, Tucson, Ariz., 1984. In this process, the simple cyanides and heavy metals, such as copper, zinc and nickel cyanides, are oxidized to non-toxic cyanates. The hydrogen peroxide process is advantageous because it adds no new substances to the environment except for oxygen and water, unlike other processes which result in salt formation and introduction of such salts to natural waterways.
In the mining industry, particularly in the precious metal processing plants, the waste effluent often takes the form of so-called tailings pulps or slurries in which the amount of solid may be as high as 50% or even higher. A pulp or slurry is formed when an ore (solid) is thoroughly mixed with water. In treating these pulps or slurries with hydrogen peroxide, the consumption of hydrogen peroxide in some cases may be too high to be cost effective. Therefore, a process which enables detoxification of cyanide containing effluents, especially pulps or slurries, with economically viable amounts of hydrogen peroxide would be welcomed in the industry.